FactoidThe augmented 4th spans four diatonic scale degrees like a perfect fourth but with an extension of a semitone. The number of diatonic degrees it spans is what distinguishes it from a diminished fifth, so C - F is a perfect fourth, C - F# is an augmented fourth, and C - F♭ is a diminished fourth

FactoidThe augmented 4th spans four diatonic scale degrees like a perfect fourth but with an extension of a semitone. The number of diatonic degrees it spans is what distinguishes it from a diminished fifth, so C - F is a perfect fourth, C - F# is an augmented fourth, and C - F♭ is a diminished fourth